The advent of local area networks suitable to interconnect multiple work stations or personal computers for communication or resource sharing purposes has proliferated the installation of computer electrical cabling systems. A communication network or system of particular interest and expanding popularity is known as the token ring architecture. The network is characterized by a closed loop information transmission path.
The electrical cables used within a token ring type local area network utilize end connectors with normally closed shorting bars. The shorting bars disconnect upon mating of the cable connector. Once mated into a token ring network the whole of the cable becomes an element in the transmission path of the token ring network, the shorting bars providing the return path from unmated cable ends. In this preferred and presently commonly utilized token ring network the cable is comprised of four electrically distinct wires which under the influence of the shorting bars loop in pairs.
The token ring cables are used in local area networks which extend not only within defined office areas or floors of buildings, but are fully capable of being routed throughout an extended structural complex. Experience with such cables has shown that the tags routinely used to identify the corresponding ends of cables are often missing, damaged or incorrectly marked. Also, multiple cables are frequently installed during the same time and without end connectors. Consequently, the identification of matching cable ends has become a reoccurring problem for the electricians or technicians connecting the local area networks. The presence of shorting bars in unmated cable connectors, and the impedances or voltages generated by the computers connected into token ring networks, further complicate the identification of cables added into existing networks.
U.S. Pat. No. 4,471,293 describes a cable tester for evaluating continuity and shorting. Both ends of the cable under test must be connected to the workbench style test unit. U.S. Pat. No. 4,556,839 relates to a power line identifier in an AC wiring system. Line identification is accomplished by creating pulsating loads at one end of the line and detecting current surges at intermediate line locations. Another potentially related U.S. patent is U.S. Pat. No. 4,703,497, directed to a telephone cable tester. However, the tester is not configurated to identify cables nor is the tester operable in the context of a cable which has selectively shorted connector ends. International Business Machines (IBM) Corporation manufactures and sells a cabling system tester identified as Part No. 4760501, or in a kit as Part No. 4760500. The IBM unit is designed to test the token ring multistation access unit (MAU) operation or, in the case of a token ring cable connected to the MAU, the combination of the MAU and cable continuity. A portable MAU tester and initializer unit is also available from NCR Corporation, under the identification S/N 902-0010108. The NCR unit incorporates a token ring cable connector which when mated to the MAU will initialize the coil latching relay in the MAU. MAU relay operation is confirmed by the relay noise associated with switching. In contrast to its combined use in the present invention, the standard NCR MAU tester and initializer unit does not include internal shunting by jumper wire across selected connector pins.
Consequently, there exists a need for a portable device which identifies corresponding cable ends, is not misled by cable connectors having shorting bars, includes a capability to concurrently evaluate the continuity of the cable lines, does not erroneously respond to low level voltages inadvertently present on cables, and includes a selftest capability. Moreover, in contrast to the relatively complex apparatus in the prior art, the portable cable identifier and tester assembly should be operable by a single individual with minimum understanding of the cable characteristics, of the work station or personal computer signal characteristics, or of the local area network configuration.